M.S. Shunmugam

Selection of optimal conditions in multi-pass face-milling using a genetic algorithm

In a Computer-Aided Process Planning (CAPP) system, one of the important steps is the selection of machining parameters which yield optimum results. In this paper, a face-milling operation has been considered. The machining parameters such as number of passes, depth of cut in each pass, speed and feed are obtained using a genetic algorithm, to yield minimum total production cost while considering technological constraints such as allowable speed and feed, dimensional accuracy, surface finish, tool wear and machine tool capabilities.

On assessment of geometric errors

SUMMARY Measurements are carried out on engineering components and analysed to check the conformity of the components to specification. This paper discusses different methods that are useful for assessing the errors on the dimensions, form and position of geometric features. A new approach called the median technique, which gives minimum values of errors is introduced.

Evaluation of circularity from coordinate and form data using computational geometric techniques

Data for evaluating circularity error can be obtained from coordinate measuring machines or form measuring instruments. In this article, appropriate methods based on computational geometric techniques have been developed to deal with coordinate measurement data and form data. The computational geometric concepts of convex hulls are used, and a new heuristic algorithm is suggested to arrive at the inner hull. Equi-Distant (Voronoi) and newly proposed Equi-Angular diagrams are employed for establishing the assessment features under different conditions. The algorithms developed in this article are implemented and validated with the simulated data and the data available in the literature.

New approach for evaluating form errors of engineering surfaces

Abstract Manufactured features generally deviate in size, form and relations with respect to other features from the features desired by the designer. Designers specify certain limits for these deviations that depend on functional requirements. The specification of different form errors is dealt with by the International Organization for Standardization (ISO). ISO also specifies that an ideal geometric feature must be established from the actual measurements such that the maximum deviation between it and the actual feature concerned is the least possible value. In practice, the least squares (LS) method is sometimes used for establishing the ideal feature, as this method is based on sound mathematical principles. However, the least squares procedure does not yield a minimum value. Therefore some attempts have been made to arrive at a form error based on the minimum deviation (MD) principles. A stray peak or valley on the actual feature introduces considerable variation in the results obtained by the minimum deviation method. This paper suggests a new approach based on the minimum average deviation (MAD). In this method, the ideal feature is established by using a search technique for different geometric features such as straight lines, circles, planes, cylinders and spheres. Using simple numerical examples, the values obtained by this approach are compared with the values obtained by the least squares and minimum deviation methods.

Surface modification in electrodischarge processing with a powder compact tool electrode

Abstract During electrodischarge machining (EDM) the topography and metallurgical and physicochemical properties of the surface layer change considerably. Under certain conditions, the metal transfer from the tool electrode to the machined surface is also appreciable. By employing suitable process parameters, surface modification for desired functional behaviour is possible by EDM. In this paper, the metal transfer from the tool electrode is studied by cross-sectional examination, electron spectroscopy for chemical analysis and X-ray diffraction analysis of the work surface. The associated changes in the surface topography are analysed by scanning electron microscopy and the harmonic contents of the surface profiles.

An algorithm for form error evaluation: using the theory of discrete and linear Chebyshev approximation

Abstract ISO defines form error based on the concept of minimum zone, but does not describe the methods to obtain the same. In this paper, drawbacks of the available methods are discussed and a new algorithm is presented. This algorithm is guaranteed to give the minimum value of form error. The algorithm is well-suited for implementation on a computer which may be interfaced with a Coordinate Measuring Machine.

Evaluation of straightness and flatness error using computational geometric techniques

The Coordinate Measuring Machines capable of automated measurement are being widely used in on-line and off-line inspection. The measurement data obtained from these inspection devices have to be further processed and analyzed, to assess the geometric form of the manufactured components. In the present work, algorithms based on Computational Geometric techniques have been developed for minimum zone and function-oriented evaluation of straightness and flatness. The algorithms are validated using the simulated data and the data available in the literature.

Data mining applied to wire-EDM process

Abstract Wire-EDM is a highly complex process, which is characterized by non-linear behavior. Due to a large number of input parameters, a data mining approach based on machine learning is followed in this paper to model this process. The model was trained on experimental data collected from carefully conducted experiments. The model was also tested on additional data. It is found that the model built using data mining provides results with desired accuracy. The important parameters have been identified and reported.

Evaluation of circularity and sphericity from coordinate measurement data

Abstract The coordinate measuring machines (CMMs) have proven to be reliable, flexible and very much suitable for determining the acceptability of manufactured parts. In this paper, techniques for evaluating circularity and sphericity error from CMM data are presented. The form error can be evaluated directly from CMM data by employing circle/sphere as assessment features and using normal deviations. The CMM data can also be transformed by applying appropriate methods that not only suppress the size but also introduce distortion. The form error is evaluated from the transformed data by employing limacon/limacoid as assessment features and using linear deviations. The methods for handling CMM and transformed data are given in this paper. The proposed methods are validated using the data available in literature.

Improvement of wear resistance by EDM with tungsten carbide P/M electrode

Abstract Electrodischarge machining with pulsing relaxation generator using a powder compact electrode and reverse polarity setting modifies the surface properties of a machined surface greatly. Using a hard and wear-resistant material in the compact, the wear resistance of the resultant surface can be improved. In the present investigation, tungsten carbide powder is used in the compact. The wear resistance is evaluated by cutting tests and the results show considerable improvement over the uncoated surfaces.